To allow accurate calculation of fuel injection amounts in an internal combustion engine it is necessary to first accurately determine the mass air flow rate. When the air rate is known, the fuel amount is calculated according to a desired air/fuel ratio. To allow rapid response of fuel control to air flow transients, the mass air flow must be determined with minimum delay.
Commonly, hot element anemometers are used as air flow meters. In many cases, these meters have a slow response time and thus do not rapidly track air flow transients. Moreover, a characteristic of such thermal devices is that the response time varies with the air flow rate, higher air flow rates yielding faster response times. Thus the amount of delay or error in the meter output depends on the air flow rate.